Processes for fabricating a semiconductor device variously include a lithography process, an etching process, an ion implantation process, and the like. After completion of one process and before transfer to the following process, cleaning and drying processes for removing impurities or residues remaining on a wafer and cleaning the surface of the wafer are carried out.
In, for example, a wafer cleaning process after an etching process, a chemical solution for cleaning is supplied to the surface of the wafer, and thereafter, pure water is supplied, followed by a rinsing process. After the rinsing process, the pure water remaining on the wafer is removed, followed by a drying process for drying the wafer.
As a method for the drying process has been known, for example, a method for drying a wafer by substituting the pure water remaining on the wafer with isopropyl alcohol (IPA). However, there has arisen an issue of a collapse of a pattern formed on the wafer due to surface tension of a liquid during the drying process.
In order to solve the above-described issue, supercritical drying under surface tension of zero has been proposed. For example, a wafer whose surface is wet with IPA is immersed in carbon dioxide (a supercritical CO2 fluid) in a supercritical state inside of a chamber, so that IPA on the wafer is dissolved in the supercritical CO2 fluid. Then, the supercritical CO2 fluid having IPA dissolved therein is gradually discharged from the chamber. Thereafter, the inside of the chamber is reduced in pressure and temperature, and then, the supercritical CO2 fluid is changed to a gaseous phase, to be discharged outside of the chamber. Consequently, the wafer is dried.
However, there has arisen an issue that when carbon dioxide is changed from the supercritical phase to the gaseous phase by reducing the pressure inside of the chamber, IPA remaining inside of the chamber in the state dissolved in the supercritical CO2 fluid is coagulated and adsorbed again on the wafer, thereby producing particles (drying stains). Moreover, in order to satisfactorily discharge IPA dissolved in the supercritical CO2 fluid from the inside of the chamber, the supercritical CO2 fluid is necessarily continued to be supplied to the chamber, and further, the supercritical CO2 fluid having IPA dissolved therein is necessarily continued to be gradually discharged in a small quantity, thereby raising an issue that a time required for the drying process becomes longer.